Represents the "DPartRootNode" entry of the dpartroot dictionary object.

It is a required entry defined as part of the PDF 2.0 specification.

It contains a DocumentPartElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 408, page 829.

The DPartRootNode entry references the root node of the document part hierarchy tree. All document part nodes are descendants of this root, and processors begin traversal here.